Workers at Canadian company Sherritt International's Ambatovy nickel project in Madagascar are considering industrial action over fears of potential job losses.
Ambatovy project is claimed to be one of Madagascar's biggest foreign investment projects, Reuters said.
When Madagascar's parliament voted in May to sack president Hery Rajaonarimampianina, the state faced a political crisis.
The union's legal department head Richard Rakotovao told the news agency: "We could go up on strike, but we have to be careful before deciding to move in this direction."
Rakotovao said that the workers are worried about job cuts.
Earlier this year, workers at the mine went on strike.
In April, the mining company managed to achieve its target production rate ahead of schedule, posting a rise of 11% in quarterly revenue as it increased production.
Sherritt International owns a 40% interest in the Ambatovy venture.
With mine life estimated at 29 years, Ambatovy has a production capacity of 60,000t of nickel and 5,600t of cobalt a year.
The mine is a joint venture between Sherritt, Sumitomo (27.5%), Kores (27.5%), and SNC-Lavalin (5%).
Located in the Alaotra Mangoro region the mine is set on two nickel deposits including the Analamay and Ambatovy deposits and has estimated reserves of 125 million tonnes of ore.
Image: Ambatovy has a production capacity of 60,000t of nickel. Photo: courtesy of Ambatovy.